Modern semiconductor industry requires smaller and smaller integrated circuits, more and more integrated, and moves forward in accordance with Moore's Law. The internal drive is to continually deepen the development of lithography. Since 1980s, lithography has been developed from I-line (365 nm) to deep ultraviolet (DUV, 248 nm and 193 nm), as well as the most attractive next-generation of extreme ultraviolet (EUV, 13.5 nm); the corresponding photoresist system will also be developed.
Photoresists used for 193 nm lithography are mainly polymer systems. As a photolithography technique requires resolution, sensitivity and line edge roughness continually being improved, 193 nm lithography has been difficult to achieve. Meanwhile, since the extreme ultraviolet lithography uses the light source of 13.5 nm only, 32 nm and 22 nm nodes can be achieved, and even lower technology nodes, which means that EUV lithography will play a very important role in the future lithography field. Because EUV lithography has different characteristics from other lithographies, the corresponding photoresist material also will have more stringent requirements. EUV photoresist requires a low extinction rate, high transparency, high etching resistance, high resolution (less than 22 nm), high sensitivity, low exposure dose (less than 10 mJ/cm2), high environmental stability, the low-yield gas and low line edge roughness (less than 1.5 nm), and so on. Therefore, the existing polymer systems are not able to achieve the requirements of EUV lithography due to high molecular weights and inhomogeneity. Thus the development of novel photoresists become important.
Molecular glass is a small molecular organic compound with a higher glass transition temperature (Tg). It combines the advantages of polymer and small molecule: low molecular weight, monodispersity, amorphous, high thermal stability, having a specific glass transition as polymer compounds, which shows that it is a class of desirable photoresist material. Since the molecular glass photoresist has excellent performance, it can not only be used in conventional 248 nm and 193 nm lithography, but also more likely to be preferred compounds of the subject material in the next-generation lithography technology (such as EUV lithography, nano-imprint lithography and e-beam carved, etc.).
Relatively conventianl molecular glass photoresists are polyphenolic photoresists and calixarene photoresists. Through different levels of protection (such as protected by a tert-butoxycarbonyl protecting group or an adamantyl group) to their active hydroxyl groups, and formulation with photoacid generators, cross-linking agents, photoresist solvents and other additives, positive or negative photoresists with different properties can be obtained.